Antimicrobial composition supported on a honeycomb shaped substrate

ABSTRACT

An inorganic antimicrobial composition has the formula AB2O4, wherein A and B are low temperature far infrared irradiating metals, A is Mg, Zn, Mn, Ni, Co, or Fe(II), B is Al, Cr(III), Mn(III) or Fe(III), and O is oxygen. An antimicrobial article is made by coating said composition on a porous honeycomb-shaped substrate. An organic antimicrobial article is made from a quaternary ammonium salt coated on a porous honeycomb-shaped substrate. Processes of making the antimicrobial articles are provided.

This is a division of an allowed application, Ser. No. 09/356,549 filedon Jul. 19, 1999 now U.S. Pat. No. 6,251,417, which is a division ofapplication of Ser. No. 09/046,834 filed on Mar. 25 1998 now U.S. Pat.6,051,246 which claims foreign application priority of an early filedTaiwan application No.86103892, which was filed Mar. 28, 1997, nowabandoned. A certified copy of the Taiwan application was submitted inthe first prior application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a novel antimicrobial inorganic compositionand articles coated with the inorganic composition,and an organicantimicrobial composition, and a process of making such articles. Morespecifically, it relates to a composition comprising low temperature farinfrared irradiating metals supported on a porous honeycomb shapedsubstrate, and an organic quaternary ammonium salt bonded on a poroushoneycomb-shaped substrate.

2. Prior Art

Antimicrobial metals have been known to be incorporated into paints andfibers for industrial or home applications. Organic quaternary ammoniumsilane has been shown to have anti-algae properties. The followingpatents show the use of silver, copper, and zinc in antimicrobialsubstances, and the use of organosilicon compounds.

U.S. Pat. No. 3,865,728 discloses an organosilicon compound coated on afibrous substrate and then heated to 65-100 degrees C. The resultingproduct is used for control of algae in aquarium tanks.

U.S. Pat. No. 5,147,686 discloses an antimicrobial powder made bycoating a titanium oxide substrate with antimicrobial metals includingcopper, zinc or alloys of Cu-Zn, Cu-Ag, Cu-Al, Cu-Sn or the combinationof these metals. The composition is useful against variousmicroorganisms such as E. Coli, Salmonella typhimurium, and others. Thecoated substrate is fired at 400 degrees C. The powder form of thisproduct is intended to be incorporated into a resin.

U.S. Pat. No. 5,151,122 relates to an antibacterial ceramic material.Various ceramics such as zeolite or alumina or clay are described asbeing fired at temperatures as high as 1200-1300 degrees C. so as tolock in the absorbed antibacterial metals such as silver, copper, orzinc. The patent further suggests that the product can be added to aresin which can be molded into any shape.

U.S. Pat. No. 5,415,775 relates to an ultrafiltration membraneconsisting of alumina and titanium dioxide which has been sintered at1000-1500 degrees C. and then coated with metal oxide. The membraneexhibits anti-bacterial properties.

U.S. Pat. Nos. 5,618,762, 5503,840, and 5,595,750 variously show Ag, Cu,Zn. Pt, Cd, Cr as antibacterial components including protectivecoatings.

None of the above patents shows an antimicrobial composition asdisclosed herein. Furthermore, none of the above patents addresses theproblem of keeping streams, water reservoirs, public baths, and fishfarms clear of harmful micro-organisms including algae or bacteria. Inaddition to their antimicrobial properties, the articles of the presentinvention show high efficacy due to the honeycomb structure of thesubstrate which provides multitude of antimicrobial sites per unitvolume and prolonged antimicrobial efficacy in flowing air or water dueto strong adhesion of the antimicrobial component on the substrate,without any adverse environmental effects such as are encountered whenchemical pesticides, bactericides or herbicides are used.

The object of this invention is to provide antimicrobial articles havingcoated thereon a novel metal composition or an organic quaternaryammonium salt according to a specific process to eliminate harmfulmicrobes such as E. coli, Salmonella typhimurium, and Saccharomycetessuch as Saccharomyces cerevisiae, Candida albicans; Algae groups,such asBlue Green Algae, Brown Algae, and Green Algae, and Bacteria such asChaetomium globosum, Penicillium funiculosum including Legionellapneumophila. Another object is to provide inexpensive articles havingthe shape of porous honeycombs treated with the antimicrobial substancesof this invention. Such articles can be placed in nets or cages instreams, rivers or stationary bodies of water to eliminate harmfulmicrobes. Still another object is to provide methods to prolong the lifeof such articles, thereby increasing and prolonging antimicrobialeffectiveness. These objects of the invention will become apparent fromthe following description.

SUMMARY OF THE INVENTION

The articles of this invention are porous honeycomb-shaped substrateshaving coated theron inorganic or organic antimicrobial components. Theinorganic component is selected from the Low Temperature Irradiating FarInfrared Material, herein referred to as metal composition. Said metalcomposition comprises metals capable of emitting far infrared radiationhaving a wavelength of from 3 to 30 microns below 60° C., whicheliminates microbes. The metal composition has the general formula:AB₂O₄ of a regular spinel structure. It is to be noted that A and B arenot chemical symbols. A is magnesium, divalent iron, nickel, manganese,cobalt or zinc. B is aluminum, trivalent iron, trivalent manganese, ortrivalent chromium. O is oxygen. The composition may contain one or moreof the following compounds: ferric oxide, ferric sulfide, zinc oxide,calcium oxide, titanium oxide, cupric oxide, aluminum oxide, aluminumsulfide, strontium oxide, and tantalum oxide as impurities.

The organic antimicrobial component is a quaternary ammonium salt havingthe formula:

wherein m+n is 16 to 19, m is to 6, and n is 13 to 17; or m+n is 20 to23, m is 4 to 11 and n is 9 to 17, X is halogen; and Y is a hydrolyzableradical or hydroxy group.

The porous substrate of the antimicrobial article in accordance withthis invention is sodium silicate, or diatomaceous earth or a ceramicmaterial or siliceous clay or material comparable to silicon dioxide oraluminum oxide, which has been made into a honeycomb structure either bymolding or extruding. The substrate is impregnated with either one ofthe above antimicrobial substances and calcined at a predeterminedtemperature.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the survival rate of the bacteria in accordance with theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The Inorganic Antimicrobial Article

The substrate of the antimicrobial article is made of siliceous clay,ceramic or Boehmite powder mixed with water to form a slurry andextruded into a honeycomb-shaped preformed substrate having highporosity.(herein referred to as preformed substrate). This preformedsubstrate has about 400 cells per square inch, providing a large surfacearea for the deposition of antimicrobial material. An alternativesubstrate may be made from a polymer material having the honeycomb shapeand coated with the substrate material.

In fabricating the antimicrobial inorganic article using the metalcomposition as the antimicrobial component, the metal composition isblended with an appropriate bonding agent to form a soaking slurry orsolution. A preformed substrate is impregnated with the soaking slurry.

The metal composition can be MgFe₂O₄.,Zn Fe₂O₄.FeCr₂O₄.MnFe₂O₄. or anycombination of metals selected from the A and B groups.

The bonding agent to be mixed with the metal composition can be analkali metal silicate, such as sodium silicate. The metal compositionshould be 10-75%, preferably 25-50% by weight of the mixture.

Alternatively, the metal composition of this invention may be blendedwith the powder substrate directly, without soaking, and then moldedinto a honeycomb-shape, and calcined. The metal composition should be10-85% of the total weight of the mixture, preferably 25-75%. Theimpregnating process is preferred to the blending process.

The impregnated substrate is calcined at a temperature of 700-1100° C.,preferably 800-1000° C. The calcining time is not critical; it can bebased upon the size the articles.

The Organic Antimicrobial Article

Quaternary ammonium organosiloxane salt (herein referred to asquaternary ammonium salt) used as algaecide by coating on a fibrousmaterial as shown in U. S. Pat. Nos. 3,817,452 and 3,865,728 forms nopart of this invention. Rather, this invention provides a new method ofpreparing an antimicrobial article. Moreover, the article kills not onlyalgae but also bacteria. The relevant portions of the above patents areincorporated herewith by reference.

In the process of this invention, the quaternary ammonium salt isdissolved in water to form a moiety of —Si (OH)₃ and the preformedsubstrate is soaked in the solution. The moiety of the quaternaryammonium salt reacts with the SiO₂ of the substrate thereby forming astrong bond. 3-(Trimethoxysilyl)propyldimethyloctadecyl ammoniumchloride is representative of the group of is representative of thegroup of silyl quaternary ammonium salts that may be used in the instantapplication.

It has been found that in the process of making the organicantimicrobial article of this invention, a special calcining aid can beused to enhance the adhesion or bonding of the quarternary ammonium saltto the preformed substrate. The calcining aid is aluminum oxide withhigh pore surface per unit volume, such as Boehmite, which is availablefrom Condea Corporation in Germany. Other calcining aids can be SiO₂ orSiO₂.Al₂O₃.

In the preparation of the organic antimicrobial article, aluminum oxideis mixed with water in the ratio of 1:1 to 1:10 by weight. An acid suchas nitric, hydrochloric, or oxalic acid is added to adjust the pH to3-6. After the mixture is ground to a gelatinous solution, the porouspreformed substrate (as first described in conntection with theinorganic antimicrobial article ) is dipped into the gelatinoussolution. This calcining-aid-coated preformed substrate is then calcinedat 400 to 1500° C., preferably at 500 to 800° C.

Quaternary ammonium salt is dissolved in a solvent selected from thegroup consisting of water, alcohols, ketones, esters, hydrocarbons andchlorinated hydrocarbons in a concentration of about 0.05 to 20%,preferably 0.3 to 0.6% by weight. Water is the preferred solvent. Thecalcined substrate as prepared from above is impregnated with thequaternary ammonium salt solution until saturated or 50% of the solutionis absorbed. The impregnated substrate is then dried at 50 to 200° C.,preferably at 60 to 150° C. to form the organic antimicrobial article.Drying time depends on the size of the substrate.

The antimicrobial articles of this invention may be placed in water tokill microbes in, for example, cooling water. They may be placed incirculating air in air conditioning system to sterilize the air. After aperiod of use, the articles may be regenerated by flushing with cleanwater or vibrated with a ultrasonic device to remove any accumulateddebris.

The following examples illustrate the preparation of the antimicrobialarticles of this invention and their efficacy.

EXAMPLE 1

Preparation of the Inorganic Antimicrobial Articles

25 parts by weight of the metal composition MgFe₂O₄ and 75 parts byweight of 35 weight percent sodium silicate solution are mixed to form auniform slurry, which is used to impregnate the preformedhoneycomb-shaped substrate. Excess suspension is drained and theremainder dried by air blowing. The coated substrate is calcined at800-900° C.

EXAMPLE 2

Process for Producing Inorganic Antimicrobial Articles

The metal composition ZnCr₂O₄ is mixed with powder substrate and sodiumsilicate in a 3:1 ratio by weight in the presence of an appropriateamount of water, forming a slurry, which is molded into honeycomb shape,and calcinied at 900-1100° C. to produce the inorganic antimicrobialarticle.

EXAMPLE 3

Process of Producing Organic Antimicrobial Article

Into 100 ml. of 0.5 wt. % aqueous solution of3-(trimethoxysilyl)propyldimthyloctadecyl ammonium chloride, there isdipped a 50g. piece of the porous preformed substrate to soak untilsaturated. At least 50% of the solution should be absorbed. The piece ofsoaked substrate is dried at 100° C. for about 30 min. to allow chemicalbonding to occur.

EXAMPLE 4

Test for Bonding Strength for Inorganic Antimicrobial Article (MetalComposition Coated on Porous Preformed Substrate)

A uniform soaking slurry of the metal composition was made according toExample 1. The dry weight (A1) of each of the ten 10 pieces of thepreformed substrate of about the same dimensions from the same batch wasrecorded The substrate pieces were soaked in the soaking slurry. All thesoaked pieces were calcined under same conditions as described in theExample 1. The weight of each piece of the calcined substrates wererecorded as (A2). The incremental weight, (A2−A1), represents thecoating weight. The calcined substrate pieces were placed in anultrasonic wash tank and subjected to vibration for one minute under 75Wpower input and dried. Each substrate piece was weighed as weight(B).(B−A1) is the coating weight after vibration. The percent of adhesion ofthe coating equals (B−A1)/(A2−A1)×100. The calculated result is shown inTable 1.

TABLE 1 Sample Percent adhesion 1 97 2 98 3 99 4 99 5 99 6 98 7 99 8 1009 99 10 98 Average 98.6

EXAMPLE 5

Test for Adhesion of Coating on Organic Antimicrobial Article.(Quaternary Ammonium Salt on Substrate)

Bromophenol blue changes color from violet to light blue to dark bluedepending on the concentration of quaternary ammonium salt present inthe water. A series of ten color standard solutions was prepared bydissolving the quaternary ammonium salt in the amount of 0,0.1,0.25,0.5,1.0, 2,5,5,10,15, and 20 wt. %×10 ⁻⁴ in 500 cc of water. Afixed amount of bromophenol is added to each of the standard solutionsto develop a series of color standards to which the sample is compared.

Ten samples of the organic antimicrobial articles were prepared as inExample 3 and the coated salt weight of each sample was recorded byweighing the coated, calcined article and the preformed substrate. Thesamples were placed in ten beakers. To each of the beakers, 500 cc ofwater were added. Each beaker was subjected to succesive ultrasonicvibration as in Example 4 for 0.5, 1, 2, 5, 10, 20, and 30 hours. Aftereach interval of vibration, the vibration operation was stopped; thesample was taken out of each beaker and rinsed. To the remainingsolution in each beaker, the same amount of bromophenol blue as used inthe standard solution was added to develop different colors. Thisdeveloped color is compared with the standard to determine theconcentration of the quaternary ammonium salt dissolved. After eachsample is initially vibrated for 0.5 hr, the sample was rinsed andimmersed into its beaker filled with fresh water and subject tovibration for a subsequent period, i.e. 1 hr. Again the dissolvedquaternary ammonium salt was determined likewise. This procedure wasrepeated for each sample until the 30-hr vibration. The results areshown in the following table.

TABLE 2 Time, Hr. 0.5 1 2 5 10 20 30 sample % of Quaternary AmmoniumSalt Dissolved 1 1.0 0.5 0.5 0.5 0 0 0 2 0.5 0.5 0.5 0.5 0 0 0 3 0.5 0.51.0 0 0 0 0 4 1.0 0.5 0.5 0 0 0 0 5 0.5 0.5 1.0 0.5 0 0 0 6 1.0 0.5 0.50.5 0 0 0 7 0.5 0.5 0.5 0.5 0 0 0 8 0.5 0.5 1.0 0.5 0 0 0 9 0.5 0.5 1.00 0 0 0 10  0.5 0.5 1.0 0.5 0 0 0 Average 0.65 0.5 0.75 0.35 0 0 0

Note: The % of quaternary ammonium salt dissolved is based on theoriginal weight coated salt.

It is seen that the coated salt according to this invention initiallyloses under two percent on average and after 10 hour vibration, nothingis dissolved and about 98% the salt remains coated on the preformedsubstrate.

EXAMPLE 6

Efficacy of Inorganic Antimicrobial Article

Water samples from the pond of a fish farm were collected. The water wasclear but some algae were growing at the bottom of the pond. The waterwas filtered with gauze. Four aquarium tanks 30 cm×20 cm×25 cm (length,width, height) numbered A, B, C and D were each filled with about 12liters of the filtered water with the level of the water at 20 cm.

In tank A and C, the inorganic antimicrobial article having the metalcomposition coated thereon as described in Example 1 were placed, whiletanks B and D received no inorganic antimicrobial article. The fourtanks were left outdoors exposed to full sun. The tanks were coveredwith a sheet of transparent glass to prevent objects from falling inwhile allowing air to pass through.

Every other day a 30-cm ruler with 1 mm divisions was inserted into thewater to observe and measure the variation and depth of visibility. Theresults are shown in Table 3.

TABLE 3 Time, days 1 3 5 7 9 11 13 15 17 Tank Visibility, in cm fromsurface of water A 20 20 20 20 20 20 20 20 20 B 20 20 16-18 12-15 8-94-5* *** *** *** C 20 20 20 20 20 20 20 20 20 D 20 20 15-18 12-14  7-8*4** *** *** *** *small amount of moss on tank wall. **moss grew on tankwall, but not covered fully ***tank wall full of moss Tanks A and C werefree of moss after 3 months.

EXAMPLE 7

Efficacy of Organic Antimicrobial Article

Escherichia coli, Salmonella typhimurium and Legionella pneumophila wereincubated at 35° C. for 24 hours and the cell counts were determined.The antimicrobial articles as prepared in Example 3, and subjected to 10hr. ultrasonic vibration. These treated articles and one preformedsubstrate were sterilized in an oven at 100° C. for 3 hours.

The three prepared porous articles were then hung in three sterile500-mi beakers with magnetic stirring rods placed at the bottom. 500 mlof water-diluted cell suspension (around 2.0×10⁷ CFU/ml) of each of thebacteria was poured into the beakers. The suspension was then stirred tocreate a swirl on top of the liquid. Cell counts of the suspensions weremade at 0, 10, 20, 30, 40, 50, 60 and 70 minutes.

A control experiment was made with the sterile preformed substratewithout coating of the quaternary ammonium salt. The substrate wassuspended in a sterilebeaker provided with magnetic stirring rod. A 500ml. of water with 2.0×10⁷ CFU/ml of Legionella pneumophila was added tothis beaker. All the beakers are incubated under same conditions.

The survival curve of Escherichia coli, Salmonella typhimurium andLegionella pneumophila suspended in water in the presence of theantimicrobial articles of this invention is shown in FIG. 1. The controlis shown as diamond in FIG. 1.

FIG. 1 shows the survival rate of each bacteria. Legionelia pneumophiladies within 10 minutes in contact with the antimicrobial article. E.coli dies after 40 minutes and Salmonella typhimurium after about 60minutes. The control show the same rate of survival of Legioneliapneumophila.

The novelty of the antimicrobial articles of this invention has beenillustrated firstly in a new metal composition of which the irradiatingproperty exhibits antimicrobial power which does not rely on physicalcontact in order to kill microbes; secondly in a new process of adhesionof antimicrobial components on a porous honeycomb-shaped substrate, andthirdly, the antimicrobial effectiveness of the articles of thisinvention is against many species of microbes.

The foregoing is considered illustrative of the principles of thisinvention. Numerous modifications and changes may occur to those skilledin the art. It is not desired to limit the invention to the specificexamples as described. Accordingly, all suitable modifications fallwithin the scope of the appended claims.

What is claimed is:
 1. A process for producing a porous antimicrobialarticle comprising a. mixing a powder of 10-80% weight % of a metalcomposition having the formula AB₂O₄, wherein A is selected from thegroup consisting of magnesium, divalent iron, manganese, nickel, cobaltand zinc; B is selected from the group consisting of aluminum, trivalentiron, trivalent manganese and trivalent chromium; and O is oxygen with apowder substrate to form a mixture; b. adding water to the mixture toform a slurry; c. molding the slurry into a honeycomb-shaped article;and d. calcining the article at 700-1100 C.
 2. The process of claim 1wherein the substrate is selected from the group consisting of siliceousclay, ceramic, aluminum oxide and the combination thereof.
 3. Theprocess of claim 1 where the calcining temperature is 800-1000° C.